1. Field of the Invention
The present invention relates to a method and an apparatus for printing an image using a liquid developer, and particularly relates to a method and an apparatus for printing an image in which transfer property of the developed image from the image retaining member to a print medium is excellently improved.
2. Related Art
In recent years, the value of a method of forming and printing an image using a liquid developer according to electrophotographic or electrostatic technologies has been re-evaluated, because it has advantages that are not fulfilled by the method utilizing a dry developer. Specifically, since the liquid developer is of the construction that toner particles are dispersed into a carrier liquid, extremely fine toner particles of submicron size are possibly employed. Therefore, in comparison with the image forming method of the dry development type, that of the liquid development type is advantaged mainly in that it can realize a high quality image, that it is economical since a sufficient image density is obtained by a small amount of toner, and that the realistic feeling comparable to the printing (specifically, offset printing) can be actually realized.
In the conventional electrophotographic image printing method of the liquid development type, a visible image developed on the surface of the latent image retaining member provides the final image by carrying out the electrophoresis in a carrier liquid through an electric field and by directly transferring the visible image to a print medium such as a paper or the like, or by transferring it once to the intermediate transfer medium before transferring it to the print medium.
However, such a transferring method by electrophoresis causes problems that the transfer efficiency of toner image is low, resulting in disordered image.
On the other hand, as a method of transferring a visible image developed on the surface of a latent image retaining member to a print medium, there is a method in which the latent image retaining member and the intermediate transfer medium are arranged to contact with one another under pressure, so that the developed visible image is transferred to the intermediate transfer medium by utilizing the pressure (and heat), which is disclosed in Japanese Patent Application Publication No. 46-41679, Japanese Patent Application Laid-Open No. 62-280882 and U.S. Pat. No. 5,650,253. The visible image is then subsequently transferred from the intermediate transfer medium to the paper. Alternatively, there is another transferring method in which the latent image retaining member is contacted with a sheet of paper under pressure so that the toner image is transferred direct to the paper by similarly utilizing the pressure (and heat). The transferring methods proposed in the above disclosures are superior to the transferring method using electrophoresis in the viewpoints of the transfer efficiency of the toner image and image deterioration at the time of transferring, and a higher quality image is thus obtained thereby.
Although these proposals have been employed, there is still a practical problem remaining, as follows.
Namely, in the case where a toner layer constituting the visible image is as thin as the thickness in the range from submicron to a few micrometers as in the image formation method using a liquid developer, if a paper whose surface is coarse such as PPC (Plain Paper Copier) paper or the like is used as a recording medium, the toner layer gets into the concave portions of the coarse paper under the pressur for transfering. As a result, the image density is reduced and the image quality is deteriorated.
An object of the present invention is to provide a method and an apparatus of printing an image which are capable of providing a high quality image even on the cheap paper having a coarse surface in a long term, while employing a transferring system utilizing the pressure.
In order to achieve the above-described object, the method of printing an image on a print medium with a liquid developer which comprises a liquid carrier and a toner dispersed in the liquid carrier, according to the present invention, comprises: forming a toner image comprising the toner, from the liquid developer; transfering the toner image to the print medium under pressure; and controlling the toner image to be transferred to the print medium, to adjust the complex viscosity coefficient of the toner forming the toner image to be transferred, to a value satisfying the formula: 1xc3x97104 less than xcex7 less than 1xc3x97106, wherein xcex7represents the complex viscosity coefficient (Paxc2x7s) of the toner.
The apparatus for printing an image on a print medium with a liquid developer which comprises a liquid carrier and a toner dispersed in the liquid carrier, according to the present invention, comprises: an image formation system which forms a toner image comprising the toner, from the liquid developer; a transfer mechanism which is arraged to transfer the toner image to the print medium under pressure; and a temperature controller which controls the temperature of the toner image to be transferred to the print medium to adjust complex viscosity coefficient of the toner forming the toner image to be transferred to the print medium to a value satisfying the formula: 1xc3x97104 less than xcex7 less than 1xc3x97106, wherein xcex7 represents the complex viscosity coefficient (Paxc2x7s) of the toner.